Typical tire curing presses include a center mechanism which provides the primary interaction between the press and a green tire being processed by the press. While various types of center mechanisms have been developed over the years, the most common include a flexible, generally cylindrical bladder that is secured to the press and insertable within a green tire. These bladders may be radially distended in order to apply shaping and curing pressure as well as heat to the interior of the green tire. These center mechanisms are also capable of stripping the bladder from the tire after the curing process is completed.
In the past, the operation of a center mechanism bladder in conjunction with conventional bias-ply tires was relatively simple due to the cylindrical form of the uncured tire. Radial-ply tires, however, require more complex bladder manipulation. Green radial tire carcasses must be at least partially preformed before the breaker ply is positioned and affixed. Thus, prior to cure, the green tire approximates, to a substantial extent, the configuration of the cured tire. As a result, the bead-to-bead interior profile dimension of a green radial tire substantially exceeds the axial distance between the beads. Therefore, a bladder or bag that has an axial extent that approximates the bead-to-bead dimension will project a substantial distance above the upper bead of the tire when extended axially upwardly to receive the green tire. In such instances, controlled movement and positional monitoring of the upper and lower bead area of a bladder is significant in accurately concentrically locating the bladder within the tire to complete shaping and curing of a green radial tire.
Accurate placement and positional control of the bladder within a green tire is important to the eventual uniformity and performance of the resulting cured tire. It is advantageous to control not only the vertical axial positions of the bladder beads, but also the relative angular or rotational movement therebetween. Prior art center mechanisms fail to inhibit relative angular or rotational movement between the bottom and top bladder beads, which can lead to nonuniformity and other quality issues. Still other weaknesses in prior art center mechanisms include inaccurate positional measurement of the top and bottom bladder bead rings, which is, of course, critical information when receiving and removing tires therefrom. Further, prior art positional measurement devices are often bulky external devices that take up excess space and are susceptible to damage. Still further, prior art center mechanisms often require multiple pressure sources to drive individual pistons for both the lower bladder bead and the upper bladder bead. This configuration inherently adds complexity and cost to the center mechanism. Thus, existing center mechanisms have all involved at least a built-in or potential disadvantage that can materially affect tire quality and uniformity.